Current models for predicting human daily energy expenditure (DEE) in both industrialized and non-industrialized populations significantly underestimate actual DEE, particularly among highly active populations. A great number of studies have examined the cost of the individual components of DEE (thermoregulation, activity, and resting metabolic rate) in laboratory settings, but few have done so comprehensively in natural environments. In this study, we provided a new model for predicting DEE and then tested it with measured DEEs of healthy, highly active adults (N=55) participating in National Outdoor Leadership School semester long courses. Two of the semester-long courses took place in both hot and temperate climates (N=25) and the other two in both temperate and cold climates (N=30). This enabled DEE measurements in a variety of climatic conditions, allowing a greater examination of the impact thermoregulatory cost has on DEE in natural environments. DEE was measured for a six-day period within each climate setting using the doubly labeled water and flex-heart rate methods. Daily food logs were kept to measure caloric intake, and daily activity logs were kept to document the type, intensity, and duration of the various activities performed by each subject. The DEE data collected from this study was then used to test the efficacy of and improve our new model for predicting DEE at any activity level in any given climate. Our new predictive model will enable us to examine the DEE of not only current human populations but also that of past hominin populations.

This research was made possible by a generous grant from the Leakey Foundation.